In a typical fine blanking apparatus, it is desirable to accurately cut and punch a slug from a workpiece. Such apparatus usually includes an upper die and a lower die, the lower die having a movable portion supporting the slug to be cut. In order to ensure the desired precision, it has been common practice to provide a delay in the movement of the lower die portion upwardly after the slug has been cut and punched from the workpiece. Such a delay has been produced by cam control or by a hydraulic system. These systems do not "delay" ascent in the sense of holding the slug supporting lower die portion in the down position, but rather slow its rise.
One object of the present invention is to provide a system for retaining the slug-supporting lower die portion in a down position for a predetermined period of time. The invention also has the capability of controlling the rise of the slug-supporting lower die portion and of stopping the rise at an intermediate position.
In accordance with the specific embodiment about to be described, the portion of the lower die supporting the cut slug is supported by at least one gas cylinder coupled to gas under pressure to cushion its downward movement and delay its upward movement. Each of the cylinders comprises a piston reciprocable within a vertical cylinder body. The piston has an upwardly extending piston rod engaging the slug-supporting portion of the lower die. The lower portion of the cylinder body beneath the piston is connected to gas under pressure. A passage connects the upper portion of the cylinder body above the piston to the lower portion of the cylinder body beneath the piston. A passage connects the lower portion of the cylinder body to a tank, and a passage connects the upper portion of the cylinder body to the tank. Valves are provided to control gas flow in the respective passages.
Further in accordance with the invention, a controller is provided for opening and closing the valves in a predetermined sequence. At the beginning of a cycle, the valve in the passage between the lower portion of the cylinder body and the tank may be open while the valve in the passage between upper portion of the cylinder body and the tank is closed, and the valve in the passage connecting the upper and lower portions of the cylinder body are closed. When the piston moves downwardly, the increased gas pressure in the lower portion of the cylinder body increases the pressure in the tank, after which the valve in the passage between the lower portion of the cylinder body and the tank is closed and the valve in the passage connecting the upper and lower portions of the cylinder body is opened to equalize the pressure therein. Then the valve in the passage connecting the upper and lower portions of the cylinder body is closed and the valve in the passage connecting the tank to the upper portion of the cylinder body is opened to transmit the increased gas pressure from the tank to the upper portion of the cylinder body and thereby hold the piston in the down position.
The controller is also capable of controlling the rise of the piston in the cylinder body and of stopping the rise at an intermediate position.
A further object of the invention is to provide a system for obtaining a predetermined time delay in a blanking machine having the foregoing features and capabilities.
These and other objects, features and advantages of the invention will become more apparent as the following description proceeds, especially when considered with the accompanying drawings.